Conventional coin return control systems for automatic vending machines are known which receive coins deposited from outside the machine and pay out coins as change when appropriate. The coin return control system normally pays out a coin from change retaining tubes each corresponding to one of a plurality of coin denominations or types from a coin paying out portion based on an instruction signal from a control portion to operate a coin return chute opening.
As shown in Japanese Patent Laid-open Gazette No. 52-82392, the coin return control system may also be provided with an auxiliary change retaining tube which corresponds to the coin type to be paid out as change. The coin denomination of coins retained in the auxiliary change retaining tube is predetermined by the setting of a coin denomination predetermination switch mechanism which includes small dip switches. A control portion detects the predetermined value of the coin denomination from the dip switches every time the vending machine is used and change is to be delivered and instructs a coin paying-out mechanism to pay out a coin via the auxiliary change retaining tube when the number of the coins which is retained in the change retaining tube of the coin type corresponding to the predetermined denomination is below a predetermined value, for example, when the corresponding change retaining tube has become empty.
That is, as shown in FIG. 1, a coin denomination is first predetermined by a coin denomination predetermination switch at step S1. The output from step S1 is input to step S2. It is determined at step S2 whether or not it is necessary for change to be paid out. If change is to be paid out, the output from step S2 is input to step S3. Otherwise, the output from step S2 returns to the input of step S1. It is determined at step S3 whether or not the coin of the coin denomination predetermined at step S1 is necessary for making change. If it is necessary, the output from step S3 is input to step S5. Otherwise, the output from step S3 is input to step S4. Consequently, a coin is paid out from an appropriate change retaining tube. In step S5, it is determined whether or not the number of the coins in the change retaining tube corresponding to the coin denomination predetermined by the coin denomination predetermining switch in step S1 has fallen to zero. If it is zero, the output from step S5 is input to step S6, and a coin is paid out from the auxiliary change retaining tube. Otherwise, the output from step S5 is input to step S4, and a coin is paid out from the change retaining tube corresponding to the coin denomination predetermined by the coin denomination predetermining switch.
In the above coin return control system, the machine may inadvertently pay out a different denomination of coin than intended since the control portion detects the predetermined value of the coin denomination predetermination switch every time change may be paid out and instructs the coin paying-out mechanism to pay out the coin from the auxiliary change retaining tube. That is, the first predetermined value of the coin type predetermination switch may be different from the predetermined value thereof after passage of a period of time because of external causes, for example, in the event a vending machine operator fails to completely set the dip switches for matching the coin denomination of the coin in the auxiliary change retention tube via the coin denomination predetermination switch mechanism or a liquid such as water invades the interior of the switch causing a faulty reading. If those causes occur, the coin return control system results in the paying out of a different denomination coin from that intended.